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Soundproofing a Wall

A little more technical than our regular posts, but understanding the technical side of soundproofing a wall is information we believe you may find helpful in your acoustics journey.

Sound is transmitted directly through a wall structure and indirectly through noise flanking paths (It occurs when noise becomes structure-borne and finds a route around an isolated surface, called a “flanking path.”).  It is important to identify the loudest noise source(s) to develop a soundproofing strategy.

There are numerous ways to soundproof a wall – the first step in soundproofing a wall is to determine the source(s) of the noise and how it gets into the room (i.e., the noise transmission paths).  

We usually use a sound level meter (SLM) to identify the noise source and its volume; an SLM is a professional-grade instrument. You can use apps for your phone as a guide; however, the SLMs are more accurate and will help achieve a more accurate result.

What is STC?

Before we begin, let us define STC – sound transmission class. STC is a rating of sound isolation of a building wall assembly. The higher the STC rating, the better sound isolation the wall assemble is to achieve.

  • 20 is considered a poor rating and
  • 60 is considered an excellent rating

Identifying the source of the noise

Once the noise source has been identified and measured, it is essential to determine the frequency content of the noise since soundproofing treatments are effective in specific frequency ranges.  The information collected will be used to create a soundproofing strategy, as follows:

  • Windows – If the offending noise source is external to the office, such as traffic noise or aircraft noise, the primary noise paths are usually the windows. Most window manufacturers offer “higher spec” windows, where they will use thicker glass.  These windows, however, will only marginally increase STC from about 28 to about 33.  It will be necessary to increase the sound transmission class (STC) of the window to be equal to or greater than the STC of the wall (in the high 30s) to achieve the desired amount of noise reduction in the space.  You can replace the windows with “acoustic windows”, which include double or triple-pane glass. These windows can provide STCs in the 50s and higher. However, they tend to be expensive.
    • Other means for reducing noise transmission through windows include the use of:
      • sonic curtains,
      • double glazing (which involves the installation of another sheet of glass on the inside of the window)
  • Doors – Interior doors have STC values in the high teens or low-20s because they are typically hollow with air gaps at the threshold and around the edges through which noise passes. Typical soundproofing measures might involve replacing the hollow core doors with solid core doors, increasing the STC to the high-20s. Acoustic drop and surround seals can be added to further increase the performance. “Acoustic doors” are also available, typically made from metal and including a significant amount of damping and absorption material inside them.
  • Ceiling – One of the most neglected sound paths includes flanking paths through the ceiling. Walls are typically built only to the height of the ceiling, which enables noise from adjoining rooms to pass into the space above the ceiling and down through the ceiling into other rooms.  We recommend extending the wall above the ceiling to the floor slab or roof structure above.  If it is impossible to extend the wall above the ceiling, we recommend installing soundproofing treatment on or within the room’s ceiling.
  • Existing Walls – Once determined that it is necessary to increase the STC of the wall, there are numerous alternatives to be considered. One method is to add additional layers of insulation and soundproof plasterboard to your walls. If that’s not feasible, covering the entire wall surface with an absorptive product like Calando Panel will lower the sound generated within the room, and therefore lower the sound that can pass through the wall.
  • New Walls – If it is possible to remove the drywall in new construction situations, many more soundproofing alternatives are available. On the base or footer of the wall, use vibration-absorbing materials to reduce the possibility of floor vibrations from travelling up the wall, transforming into sound and re-radiating into the room.  For applications such as theatres or gymnasiums where you expect very high sound levels on one side of the wall, we recommend a staggered stud arrangement. The sheet of drywall on one side of the wall is isolated from the sheet of drywall on the other side of the wall.  Additional sound attenuation can be obtained by building the wall with multiple layers of plasterboard or other sound barrier materials such as MLV and plywood and adding high-quality sound insulation in the air gap within the walls.

We understand many of these options are not the right choice for you; that is why Avenue Interior Systems specialise in retrofitting spaces to improve acoustics.

For more information on soundproofing, contact the team today on 1300 827 177.